Fibrous, non-woven, superabsorbent, ion sensitive polymer-impregnated structures are known.
See generally, U.S. Pat. Nos. 5,167,764, 5,607,550, 5,516,585 and European Publication No. 437,816. Additionally, the following references disclose previously attempted methods of handling superabsorbent or hydrogel ion sensitive polymers to obtain superabsorbent structures. See U.S. Pat. Nos. 3,669,103; 4,610,678; 4,986,882; 5,049,235; 5,137,600; 5,160,789; 5,443,899; 5,531,728; and 5,547,745. See U.S. Pat. No. 5,516,585 teaching the well known binder polymers suggested for use with air laid nonwoven structures containing SAP.
EP-A-437816 discloses a nonwoven wet-laid superabsorbent material produced by the process of blending superabsorbent, ion sensitive polymer particles with a liquid to form a slurry, mixing particles with that slurry, filtering that slurry/fibre mixture to remove a portion of the liquid and drying the superabsorbent slurry/fiber mixture to form a nonwoven wet-laid superabsorbent material.
EP-A-359615 discloses a method for the manufacture of a superabsorbent fibrous structure in which a dry solid absorbent is applied directly to a wet-laid web of cellulosic fibers prior to drying the wet web.
EP-A-273075 discloses a high water-absorbency paper made by sheeting a mixture of wood pulp fiber, water-soluble resin and high water-absorbency resin.
A number of techniques for applying binders to webs of fibers are known. For example, U.S. Pat. No.4,600,462 of Watt describes a process in which an adhesive binder is sprayed onto one or both surfaces of an air laid cellulose fiber web. Submersion of the web in the adhesive binder is another method disclosed in this patent of applying the binder. Individual binder coated fibers for mixing with other fibers are not produced by this process. A hydrophile solution is also applied to the web. As another example, U.S. Pat. Nos. 4,425,126 and 4,129,132 of Butterworth, et al. describe a fiberous material formed by combining thermoplastic fibers and wood pulp, heat fusing the combined fibers, and thereafter depositing a binder on the heat fused web. Because the fibers are heat fused prior to adding the binder, individual binder coated fibers for mixing with other fibers are not produced by this process.
Absorbent products such as diapers which include particles of a superabsorbent ion sensitive polymer such as crosslinked sodium polyacrylate disposed between layers of wood pulp are known for example from EP-A-257951.
The use of fibers of water-swellable water-insoluble superabsorbent, ion sensitive polymer is disclosed in U.S. Pat. No. 5,607,550, wherein it is taught that incorporation of superabsorbent, ion sensitive polymers in particulate form in the fiber web has significant disadvantages in many respects. The prior art teaches that superabsorbent, ion sensitive polymer particles are less securely retained both during formation of the wet-laid nonwoven structure and when the structure is in further processed during incorporation into an absorbent product. Moreover the art indicates a relatively less uniform dispersion of superabsorbent, ion sensitive polymer particles in the web occurs as opposed to the dispersion of the SAP fiber in the web. It is also taught conventionally that with superabsorbent, ion sensitive polymer particle-impregnated structures, the particles become loosely attached to the fibrous structure of the nonwoven fabric.
In order to provide sufficient absorbency performance necessaary for utilization in an absorbent article, it has been found that the loading of superabsorbent in a web must be at least about 50% by weight of the entire structure. However, significant loadings of particles in the fiber structure (such as above about 50% SAP particles on the total weight of the web) require sufficient strength of the wet web in the process
Whereas the cost associated with forming fibers of superabsorbent, ion sensitive polymer is inherently higher than that of the particulate SAP, it would be desirable to overcome the aforementioned drawbacks in the use of particles of SAP. Composite structures of fibers impregnated with superabsorbent, ion sensitive polymer particles could greatly reduce the manufacturing cost of end use products such as those aforementioned, however when forming such a structure with 50% or higher loadings of particles of SAP, the web thus formed has a rough texture which can be felt in a disposable article having a top sheet. The texture is telegraphed through the article and may provide undesirable comfort for the user.
Accordingly, there is an unmet need to develop improved superabsorbent, ion sensitive polymer particle-impregnated structures having improved texture for their intended uses. An improved superabsorbent, ion sensitive polymer particle-impregnated structure has been isolated and found to exhibit unexpected smooth texture and surprisingly good absorbency.